Perhaps one of the Air Strike series? You can apparently switch into a 2D view in them. This is Air Strike II: Gulf Thunder (2005):Aledford said:I used to play a game on PC...
I believe it was only a Demo, and I could only ever find it on the computers that were in Walmart and Staples and occasionally Best Buy (between 2006-2013).
It was a 2D (but with pretty killer graphics) top-to-bottom-scrolling, almost Arcade-style game where you flew a Helicopter and shot at bad guys. There was mostly desert terrain at first but I think you came up on some grassy areas. You could fly over/into power-ups and they would change your guns to all sorts of different patterns and rockets.
I have googled endlessly and can't ever find this game.
https://www.youtube.com/watch?v=sw4LM0UiNIM